Hitherto, many systems and a large number of apparatuses for use therein have been proposed with the purpose of obtaining multi-colored images by use of an electrophotographic process. But, in general, they can be roughly classified as follows. One of them is a method of repeating latent image formation and development on a photoreceptor by use of color toners in correspondence to the number of different colors to duplicate the colors on the photoreceptor, or carrying out transfer on a transfer material in each development to effect color duplication on the transfer material. In another system, an equipment having plural number of photoreceptors corresponding to the number of different colors is used to expose optical images of respective colors simultaneously on respective photoreceptors, developing the latent images formed on respective photoreceptors with color toners and effecting transfer successively to duplicate colors for obtaining multi-colored images.
In the former system, plural times of latent image formation and developing processes must be repeated, requiring time for picture image recording, so that there is such a large defect that it is extremely difficult to carry out such processes at high speed. Also, in the case of the one in which toner images are superimposed on the photoreceptor, since the potential lowering at the part adhered with previously developed toner is likely to be insufficient, the toner which is developed subsequently adheres to a part adhered with previously developed toner which is primarily no to adhere thereon to cause color turbidity.
In the latter system, there is such an advantage that the system has high speed due to the parallel use of a plural number of photoreceptors, but the equipment becomes complicated and too large, since it requires to have a plural number of photoreceptors, optical systems, and developing means, to result in becoming highly expensive and lacking practical applicability.
Further, in both systems, there is such a large defect that the positional agreement of picture images is difficult in the case of repeating picture image formation and transfer for a plural number of times, hence, color slippage of the picture image cannot be prevented completely.
In order to solve these problems fundamentally, it is considered to be appropriate that a multi-colored image is recorded on a single photoreceptor by effecting only one picture image exposure. However, in the actual situation, such a system has not yet been developed.